A Guide to the Natural World David Krogh © 2011 Pearson Education, Inc. Chapter 20 Lecture Outline Arriving Late, Traveling Far: The Evolution of Human Beings Biology Fifth Edition

© 2011 Pearson Education, Inc The Human Family Tree

© 2011 Pearson Education, Inc. The Human Family Tree Human evolution is the study of the taxonomic grouping called the Hominini or human-like primates. Every member of this group is referred to as a hominin, including human beings.

© 2011 Pearson Education, Inc. The Human Family Tree A common primate ancestor is believed to have given rise to both the chimpanzee and the human family evolutionary lines between 6 and 7 Mya.

© 2011 Pearson Education, Inc. The Human Family Tree The structure of the hominin tree is a matter of considerable debate among researchers. We do not have enough fossil evidence to say with certainty which species were ancestral to which others.

© 2011 Pearson Education, Inc Human Evolution in Overview

© 2011 Pearson Education, Inc. Human Evolution in Overview All the members of the hominin grouping are extinct except for Homo sapiens, the human species. Human beings were late in arriving among the hominins, but all hominins are late arrivers when the entire sweep of evolution is considered.

© 2011 Pearson Education, Inc. Human Evolution in Overview All early and mid-period hominin evolution took place in Africa.

© 2011 Pearson Education, Inc. Figure 20.2 Africa Chad Sahelanthropus tchadensis Ethiopia Kenya Orrorin tugenensis Tanzania Earliest modern human (Homo sapiens) Australopithecus fossil discoveries Paranthropus fossil discoveries Australopithecus and Ardipithecus fossil discoveries Indian Ocean South Africa

© 2011 Pearson Education, Inc. Human Evolution in Overview But in 2002, the range of likely hominin fossils was expanded 2,500 kilometers to the west, to Chad, with the discovery of the 6- to 7-Mya remains of a primitive hominin named Sahelanthropus tchadensis or Toumaï.

© 2011 Pearson Education, Inc. A Hominin Family Tree Present recent Pleistocene Millions of years ago Pliocene H. neanderthalensis H. mauritanicus H. habilis K. rudolfensis Au. africanus Kenyanthropus platyops Ar. ramidus Ardipithecus kadabba Orrorin tugenensis Sahelanthropus tchadensis ancestral primate monkeys orangutans gorillas chimps hominins Australopithecus anamensis Au. afarensis Au. bahrelghazali Paranthropus aethiopicus Au. garhi Homo ergaster P. boisei H. erectus H. cepranensis H. heidelbergensis H. floresiensis H. sapiens P. robustus Figure 20.1

© 2011 Pearson Education, Inc Interpreting the Fossil Evidence

© 2011 Pearson Education, Inc. Interpreting the Fossil Evidence In human evolution studies, molecular evidence—usually the sequencing of DNA—has increased in importance in recent years. But the primary evidence in the field remains fossil evidence.

© 2011 Pearson Education, Inc. Interpreting the Fossil Evidence Figure 20.3

© 2011 Pearson Education, Inc. Interpreting the Fossil Evidence Paleoanthropologists interpret features of fossils in order to make judgments about where a given fossil form lies in the hominin family tree. Interpretations can differ, however.

© 2011 Pearson Education, Inc. Interpreting the Fossil Evidence The two most important defining characteristics of a hominin are tooth structure and upright or “bipedal” walking.

© 2011 Pearson Education, Inc Snapshots from the Past: Four Hominins

© 2011 Pearson Education, Inc. Australopithecus afarensis The bipedalism seen in our own species clearly existed in the hominin species Australopithecus afarensis, whose most famous individual, Lucy, lived 3.18 Mya in what is now Ethiopia.

© 2011 Pearson Education, Inc. Australopithecus afarensis Lucy had a much smaller brain than modern humans do, however, and she probably was partly arboreal, or tree-dwelling.

© 2011 Pearson Education, Inc. Smaller brain Longer arms (shorter legs) Grasping feet Australopithecus afarensis Figure 20.6

© 2011 Pearson Education, Inc. Australopithecus afarensis Lucy’s set of features demonstrate that hominin features developed in a mosaic pattern—different features evolved at different points in time and in different species.

© 2011 Pearson Education, Inc. Three Hominims Figure 20.5

© 2011 Pearson Education, Inc. Homo ergaster A change to a physical form and mental capacity much closer to ours comes with the evolution of Homo ergaster, exemplified by Turkana Boy, who lived 1.6 Mya.

© 2011 Pearson Education, Inc. Homo ergaster Figure 20.7

© 2011 Pearson Education, Inc. H. erectus H. erectus was a direct descendant of H. ergaster, and the first hominin to leave Africa. Its migratory capability may have resulted in part from its anatomy, which likely allowed it to walk much the way modern humans do.

© 2011 Pearson Education, Inc. Homo neanderthalensis In their modern form, the Neanderthals (Homo neanderthalensis) populated Europe as well as parts of Asia for about 130,000 years.

© 2011 Pearson Education, Inc. Homo neanderthalensis The last of them died 28,000 years ago in Europe. The modern caricature of the caveman comes from the Neanderthals, but this image is difficult to reconcile with facets of Neanderthal life such as the burying of the dead.

© 2011 Pearson Education, Inc. Homo neanderthalensis Even given these facets, however, it is clear that the Neanderthals were a primitive species in comparison with H. sapiens.

© 2011 Pearson Education, Inc The Appearance of Modern Human Beings

© 2011 Pearson Education, Inc. The Appearance of Modern Human Beings Human beings appear to have evolved into their modern anatomical form in Africa prior to the time they began to migrate into the wider world.

© 2011 Pearson Education, Inc. The Appearance of Modern Human Beings Evidence from the sequencing of the Neanderthal genome has revealed that a small amount of interbreeding took place between Neanderthals and human beings no later than 60,000 years ago in the Middle East.

© 2011 Pearson Education, Inc. The Appearance of Modern Human Beings This interbreeding undercuts the strongest version of the “out-of-Africa” hypothesis, which holds that modern humans remained reproductively isolated from all other hominin species from the time they first evolved in Africa.

© 2011 Pearson Education, Inc. The Appearance of Modern Human Beings The initial wave of human migration out of Africa was initiated sometime between 85,000 and 55,000 years ago.

© 2011 Pearson Education, Inc. Second wave of human migration Later migration of modern humans from West Asian source, 45,000 to 35,000 years ago Europe Africa Homo sapiens fossil sites Human origins in Africa First wave of human migration Early migration of modern humans from East African source, beginning no earlier than 60,000 years ago Australia Asia The Appearance of Modern Human Beings Figure 20.8

© 2011 Pearson Education, Inc. The Appearance of Modern Human Beings The earliest fossils we have of modern human beings outside Africa and its immediate environs date from 46,000 years ago and were found in Australia.

© 2011 Pearson Education, Inc. The Appearance of Modern Human Beings Molecular evidence indicates that modern human beings evolved no earlier than 200,000 years ago. The earliest human fossils we have date from 195,000 years ago and were found in Ethiopia.

© 2011 Pearson Education, Inc. The Appearance of Modern Human Beings The arrival of modern human beings in Europe 40,000 years ago was followed by the extinction of the Neanderthals 12,000 years later. The arrival of human beings in the Far East, at least 46,000 years ago, was followed by the extinction of the Homo erectus species 6,000 years later.

© 2011 Pearson Education, Inc. The Appearance of Modern Human Beings If there is a consensus about why we human beings are the only living species of hominin, it is that we “replaced” such species as H. erectus and H. neanderthalensis by out-competing them after having migrated to Asia and Europe.

© 2011 Pearson Education, Inc Next-to-Last Standing? The Hobbit People

© 2011 Pearson Education, Inc. Homo floresiensis In 2004, researchers reported finding, on the Indonesian island of Flores, fossils of a previously unknown hominin, Homo floresiensis, who stood only 3 feet tall and seemed to have survived until 18,000 years ago.

© 2011 Pearson Education, Inc. Homo floresiensis This interpretation of the Flores fossils has been challenged, however, by two teams of researchers who have concluded that H. floresiensis actually was a small, modern human being suffering from the medical condition of microcephaly.

© 2011 Pearson Education, Inc. Homo floresiensis Figure 20.10